Unfortunately, unless you are an iTunes producer or iTunes Connect member, you can't self-publish to Apple's iBookstore.  In order to become an iTunes Connect or iBooks publisher, you have to meet the following criteria (as of 10/4/11); if much time has elapsed since this was written, check this link for updated data (or Google for "iBooks iTunes Publisher Requirements):

• An Intel-based Mac running OS X 10.5.8 or later
• At least 1 GB RAM
• QuickTime 7.0.3 or later. This is so you can encode and deliver content using our dedicated software.
• At least 10 GB of available hard drive space (more for larger catalogs) is recommended.
• A broadband internet connection with an upload rate of 1 MB/sec or faster is recommended.

You must also i) have ISBNs for all titles you intend to distribute in the ePUB eBooks format and ii) be Able to deliver book content in passing the latest version of EpubCheck.  Lastly, insofar as financial requirements, you must have
A valid U.S. Tax ID; A valid iTunes Store account, with a credit card on file, and, lastly, they want you to know that:

"Apple does not pay partners until they meet payment requirements and earning thresholds in each territory. You should consider this before applying to work directly with Apple as you may receive payments faster by working with an Apple-approved aggregator."

As shown in our ePUB Basics category, above, you can find a list of current Apple Content Aggregators here (essentially, publishers who publish your book to the iBookstore, as well as other epub and mobi channels/retailers, for a fee and a percentage of your sales):  Apple-Approved Aggregators List.

Good luck!